IPS-LCD having a third electrode having aperture and formed on counter substrate

ABSTRACT

A liquid crystal display having electrodes on a single substrate. A transparent planar electrode elongated in the transverse direction is formed on the inner surface of a substrate, and an insulating film is deposited thereon. A plurality of linear electrodes, which are elongated in the longitudinal direction and either transparent or opaque, are formed on the insulating film. Potential difference between the planar and the linear electrodes generated by applying voltages to the electrodes yields an electric field. The electric field is symmetrical with respect to the longitudinal central line of the linear electrodes and the longitudinal central line of a region between the linear electrodes, and has parabolic or semi-elliptical lines of force having a center on a boundary line between the planar and the linear electrodes. The line of force on the planar and the linear electrodes and on the boundary line between the planar and the linear electrodes has the vertical and the horizontal components, and the liquid crystal molecules are re-arranged to have a twist angle and an tilt angle. The polarization of the incident light varies due to the rearrangement of the liquid crystal molecules.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (LCD). Moreparticularly, the present invention relates to an LCD having a modifiedelectrode array.

2. Description of the Related Art

Generally, an LCD is a display having two substrates and a liquidcrystal layer therebetween. A plurality of electrodes are formed on theinner surfaces of either or both the substrates, a pair of polarizersare attached to the outer surfaces of the substrates, and the liquidcrystal layer serves as an optical switching medium. When a potentialdifference is applied to the electrodes, liquid crystal molecules arere-arranged due to the potential difference, and the re-arranged liquidcrystal molecules scatter the incident light, which have passed throughone of the polarizers, or change the transmission characteristics of thelight, thereby controlling the transmittance of the light out of theother polarizer (which is usually called an analyzer) and displayingimages.

As an example of a conventional LCD, U.S. Pat. No. 5,576,861 discloses atwisted nematic LCD (TN-LCD) where an upper electrode and a lowerelectrode formed respectively on the inner surfaces of upper and lowersubstrates and a nematic liquid crystal material is injectedtherebetween, and where the liquid crystal molecules are twisted withbeing parallel to the substrates. In the above LCD, the potentialdifference between the two electrodes generated by applying voltages tothe upper and the lower electrodes yields an electric fieldperpendicular to the substrates. The liquid crystal molecules arere-arranged such that the torque due to the dielectric anisotropy andthe torque due to the aligning treatment is balanced with each other.The torque due to the dielectric anisotropy forces the long axes of theliquid crystal molecules to be parallel to the field direction, and themagnitude of this torque depends on the intensity of the electric field.The elastic torque generated by the aligning treatment such as rubbingforces the long axes of the liquid crystal molecules to be parallel to apredetermined direction. When the director of the liquid crystal twistsby 90 degrees on going from the lower electrode to the upper electrode,and the polarization directions of the polarizers are perpendicular toeach other, the polarization of the incident light, in absence of theelectric field, rotates by 90 degrees, and thus the light passes throughthe analyzer, thereby causing white state. However, when sufficientelectric field is applied to the liquid crystal layer, since theincident light passes through the liquid crystal layer without changingits polarization, the light cannot pass through the analyzer, therebycausing black state.

As another example of a conventional LCD, U.S. Pat. No. 5,598,285discloses an LCD, where two linear electrodes parallel to each other areformed on either of the two substrates, and a liquid crystal layer liesover the region between the two electrodes, and where the liquid crystalmolecules are aligned parallel to the substrates. In this LCD, thepotential difference between the two electrodes yields an electric fieldsubstantially parallel to the substrates and perpendicular to the twoelectrodes. The liquid crystal molecules are rearranged such that thetorque due to the dielectric anisotropy and the elastical torque due torubbing are balanced with each other. When the polarization directionsof the polarizers are perpendicular to each other, in absence ofelectric field, the crossed polarizer blocks the incident light andmakes the liquid crystal display to be in black state. However, whensufficient electric field is applied to the liquid crystal layer, thepolarization of the incident light varies and the light passes throughthe analyzer, thereby causing white state.

The above-mentioned LCDs have disadvantages described hereinafterrespectively.

The principal disadvantage of the TN-LCD is its narrow viewing angle. Inthe TN-LCD, the larger an angle made by the direction of the user's eyeand the direction normal to a surface of a display, the larger the valuen d where birefringence Δn is the difference of the refractive indicesbetween in the direction of the long axes and the short axes of theliquid crystal molecules and d is the thickness of the liquid crystallayer. Accordingly, the contrast, which is defined as the luminance ofthe brightest state divided by that of the darkest state, abruptlydecreases. In addition, gray inversion phenomenon also occurs.Accordingly, the viewing angle at which the contrast is equal to 10 isvery narrow, and thus image quality is abruptly deteriorated when viewedat an angle larger then the viewing angle.

To compensate the viewing angle, methods using phase differencecompensating films are suggested in U.S. Pat. No. 5,576,861, but theyhave disadvantages in manufacturing cost and the number of the processsteps since the phase difference compensating films are additionallyattached. Furthermore, the satisfactory viewing angle may not be stillobtained even though the phase retardation compensation films are used.

The U.S. Pat. No. 5,598,285 has disadvantages in power consumption andaperture ratio. The LCD disclosed in the above U.S. Pat. No. 5,598,285has an electric field of which strength is dependent on the positions,that is, the field strength is weaker as far from the electrodes.Therefore, in order to obtain sufficient field strength at the far pointfrom the electrodes, high driving voltage is required. In addition,since all the electrodes are formed on one substrate and storagecapacitors are formed to obtain sufficient capacitance, the apertureratio is small.

In the meantime, since the liquid crystal display is a passive display,it requires an external light source. A white light is usually used forthe light source of the liquid crystal display, and red, green and bluecolor filters are used for color display. The color filters are formedon one of the substrates, and a black matrix for preventing lightleakage at the boundaries of the color filters is formed therebetween.

The light from the light source changes its properties, such aspolarization, in the liquid crystal layer, and the transmittance of thelight depends on the wavelength of the light. The transmittance alsodepends on the driving mode of the liquid crystal display.

In the case of TN LCDs, the transmittance of the blue light differs fromthose of the red and green lights by 10%. Moreover, the IPS LCD has thedifference of the transmittances of the blue, red and green lights morethan 40%.

In order to reduce the difference of the transmittance, two methods areconventionally used, one using a backlight unit and a driving circuithaving additional characteristics and the other making a cell gap to bedifferent for the pixels of different colors by adjusting the height ofthe color filters. However, the former method may increase the yieldcost and the number of process steps, and the latter may cause unevenrubbing.

SUMMARY OF THE INVENTION

An object of the present invention is to obtain a wide viewing angle.

Another object of the present invention is to reduce power consumptionof the liquid crystal display.

Still another object of the present invention is to enlarge the apertureratio.

In order to accomplish the above-mentioned objects, the array of theelectrodes of the LCD is modified.

First electrodes and second electrode insulated from each other areoverlapped with each other at least in part. The second electrode formsa continuous plane between the first electrodes, and one pixel includesat least one first electrode and one second electrode.

The potential difference between the two electrodes generated byapplying voltages to the electrodes yields an electric field. The shapeof an electric line of force is semi-ellipse or parabola having a centeron a boundary line or a boundary region between the first electrode andthe second electrode, whereby the electric field on the electrodes hasthe vertical and the horizontal components.

The liquid crystal molecules on the first or the second electrode and onthe boundary region between the two electrodes are re-arranged to have atwist angle and a tilt angle due to the vertical and the horizontalcomponents of the electric field. Therefore, the polarization of theincident light varies by the rearrangement of liquid crystal molecules.

As described above, a wide viewing angle may be obtained since theliquid crystal molecules are re-arranged to have both the twist angleand the tilt angle.

In addition, the liquid crystal molecules on the first electrode and thesecond electrode contribute to displaying images since the electricfield has the vertical and the horizontal components on the firstelectrode and the second electrode as well as on the boundary regionbetween the two electrodes.

In addition, power consumption is low since the strength of the electricfield is large on the boundary region between the first electrode andthe second electrode.

In addition, aperture ratio may be enlarged since a storage capacitorfor obtaining sufficient storage capacitance is not additionallyrequired since the two electrodes are overlapped via an insulating filmwhen using a thin film transistor (TFT) as a switching element.

Additional objects and advantages of the present invention are set forthin part in the description which follows, and in part will be obviousfrom the description, or may be learned by practice of the invention.The objects and advantages of the invention will be realized andattained by means of the elements and combinations particularly pointedout in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, illustrate embodiments of the presentinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a layout view of electrodes of a liquid crystal display (LCD)according to a first embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line II-II′ in FIG. 1,which shows both upper and lower substrates as well as equipotentiallines and lines of electrical force between the two substrates;

FIG. 3 illustrates the twist angle of liquid crystal molecules in thefirst embodiment of the present invention;

FIG. 4 is a graph illustrating the variation of the twist angle of theliquid crystal molecules as a function of the horizontal positionaccording to the first embodiment of the present invention;

FIG. 5 is a graph illustrating the variation of the twist angle of theliquid crystal molecules as a function of height according to the firstembodiment of the present invention;

FIG. 6 shows the tilt angle of the liquid crystal molecules according tothe first embodiment of the present invention;

FIG. 7 is a graph illustrating the variation of the tilt angle of theliquid crystal molecules as a function of height according to the firstembodiment of the present invention;

FIG. 8 is a graph illustrating the variation of the tilt angle of theliquid crystal molecules as a function of horizontal position accordingto the first embodiment of the present invention;

FIG. 9 is a graph illustrating the transmittance as a function ofhorizontal position in the LCD according to the first embodiment of thepresent invention;

FIG. 10 is a graph illustrating the transmittance as a function ofapplied voltage in the LCD according to the first embodiment of thepresent invention;

FIG. 11 is a graph illustrating a viewing angle in the LCD according tothe first embodiment of the present invention;

FIG. 12 illustrates the twist angle of liquid crystal molecules in thesecond embodiment of the present invention;

FIG. 13 is a graph illustrating the variation of the twist angle of theliquid crystal molecules as a function of the horizontal positionaccording to the second embodiment of the present invention;

FIG. 14 is a graph illustrating the variation of the twist angle of theliquid crystal molecules as a function of height according to the secondembodiment of the present invention;

FIG. 15 shows the tilt angle of the liquid crystal molecules accordingto the second embodiment of the present invention;

FIG. 16 is a graph illustrating the variation of the tilt angle of theliquid crystal molecules as a function of height according to the secondembodiment of the present invention;

FIG. 17 is a graph illustrating the variation of the tilt angle of theliquid crystal molecules as a function of horizontal position accordingto the second embodiment of the present invention;

FIG. 18 illustrates the twist angle of liquid crystal molecules in thethird embodiment of the present invention;

FIG. 19 is a graph illustrating the variation of the twist angle of theliquid crystal molecules as a function of the horizontal positionaccording to the third embodiment of the present invention;

FIG. 20 is a graph illustrating the variation of the twist angle of theliquid crystal molecules as a function of height according to the thirdembodiment of the present invention;

FIG. 21 shows the tilt angle of the liquid crystal molecules accordingto the third embodiment of the present invention;

FIG. 22 is a graph illustrating the variation of the tilt angle of theliquid crystal molecules as a function of height according to the thirdembodiment of the present invention;

FIG. 23 is a graph illustrating the variation of the tilt angle of theliquid crystal molecules as a function of horizontal position accordingto the third embodiment of the present invention;

FIG. 24 illustrates the twist angle of liquid crystal molecules in thefourth embodiment of the present invention;

FIG. 25 is a graph illustrating the variation of the twist angle of theliquid crystal molecules as a function of the horizontal positionaccording to the fourth embodiment of the present invention;

FIG. 26 is a graph illustrating the variation of the twist angle of theliquid crystal molecules as a function of height according to the fourthembodiment of the present invention;

FIG. 27 shows the tilt angle of the liquid crystal molecules accordingto the fourth embodiment of the present invention;

FIG. 28 is a graph illustrating the variation of the tilt angle of theliquid crystal molecules as a function of height according to the fourthembodiment of the present invention;

FIG. 29 is a graph illustrating the variation of the tilt angle of theliquid crystal molecules as a function of horizontal position accordingto the fourth embodiment of the present invention;

FIG. 30 is a layout view of an LCD according to a fifth embodiment ofthe present invention;

FIG. 31 is a cross-sectional view taken along the line V-V′ in FIG. 30;

FIG. 32 is a layout view of the LCD according to a sixth embodiment ofthe present invention;

FIG. 33 is a cross-sectional view taken along line VIA-VIA′ in FIG. 32;

FIG. 34 is a cross-sectional view taken along line VIB-VIB′ in FIG. 32;

FIG. 35A is a layout view of the LCD according to a seventh embodimentof the present invention;

FIGS. 35B and 35C are cross-sectional views taken along linesVII1B-VIIB′ and VII1C-VIIC′ in FIG. 35A;

FIGS. 36A to 39C shows intermediate structures of the LCD shown in FIGS.35A to 35C;

FIG. 40 is a layout view of the LCD according to an eighth embodiment ofthe present invention;

FIGS. 41 and 42 are two different cross-sectional views taken along lineVIIIA-VIIIA′ in FIG. 40;

FIG. 43 is a cross-sectional view taken along line VIIIB-VIIIB′ in FIG.40;

FIGS. 44 to 46 are cross-sectional views of LCDs according to the ninthembodiment of the present invention;

FIG. 47 is a cross-sectional view of an LCD according to the tenthembodiment of the present invention;

FIG. 48 is a schematic diagram of the electric field and equipotentiallines in the LCD according to the tenth embodiment of the presentinvention;

FIG. 49 is a graph illustrating the transmittance as a function ofapplied voltage in the LCD according to the tenth embodiment of thepresent invention;

FIG. 50 is a graph illustrating a viewing angle in the LCD according tothe tenth embodiment of the present invention;

FIG. 51 is a layout view of an LCD according to an eleventh embodimentof the present invention;

FIGS. 52 and 53 are cross-sectional views taken along lines XIA-XIA′ andXIB-XIB′ in FIG. 51;

FIGS. 54A to 57B shows intermediate structures of the LCD shown in FIGS.51 to 53;

FIG. 58 is a layout view of an LCD according to an twelfth embodiment ofthe present invention;

FIGS. 59 and 60 are cross-sectional views taken along lines XIIA-XIIA′and XIIB-XIIB′ in FIG. 58;

FIGS. 61A to 63B show intermediate structures of the LCD shown in FIGS.58 to 60;

FIG. 64 is a layout view of an LCD according to an thirteenth embodimentof the present invention;

FIGS. 65 and 66 are cross-sectional views taken along lines XIIA-XIIA′and XIIB-XIIB′ in FIG. 64;

FIGS. 67A to 68B show intermediate structures of the LCD shown in FIGS.64 to 66;

FIG. 69 is a layout view of an LCD according to an fourteenth embodimentof the present invention;

FIG. 70 is a layout view of an LCD according to an fifteenth embodimentof the present invention;

FIGS. 71 and 72 are cross-sectional views taken along lines XVA-XVA′ andXVB-XVB′ in FIG. 70;

FIG. 73 is a layout view of an LCD according to an sixteenth embodimentof the present invention;

FIG. 74 is a layout view of an LCD according to an seventeenthembodiment of the present invention;

FIGS. 75 and 76 are cross-sectional views taken along lines XVIIA-XVIIA′and XVIIB-XVIIB′ in FIG. 74;

FIGS. 77 to 79 are cross-sectional views of LCDs according to theeighteenth to the twentieth embodiments of the present invention; and

FIG. 80 shows an LCD according to the twenty-first embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A liquid crystal display (LCD) according to the embodiments of thepresent invention will become apparent from a study of the followingdetailed description when viewed in light of the drawings.

First, the LCD according to the first embodiment of the presentinvention is described in detail with reference to FIGS. 1 to 11.

FIG. 1 is a layout view of electrodes of an LCD according to the firstembodiment of the present invention, and FIG. 2 is a cross-sectionalview taken along the line II-II′ in FIG. 1, which illustrates both upperand lower substrates as well as equipotential lines and lines ofelectrical force between the substrates.

First, the structures of a lower substrate on which electrodes areformed and an upper substrate of the LCD are described in detail.

A planar electrode 2 made of transparent conductive material such asindium tin oxide (ITO) is formed on the inner surface of a lowersubstrate 100 made of a transparent insulating material such as glass orquartz. The planar electrode 2 has a predetermined longitudinal widthand is elongated in the transverse direction. The planar electrode 2 iscovered with an insulating film 3, and a plurality of narrow linearelectrodes 1 which are parallel to each other and elongated in thelongitudinal direction are formed on the insulating film 3. The linearelectrodes 1 may be transparent or opaque. The width of the linearelectrode 1 is equal to or smaller than the distance between the linearelectrodes 1, exactly to say, the distance between adjacent boundarylines of the two adjacent linear electrodes 1. An aligning film 4 madeof polyimide is coated all over the surface, and may be rubbed or not. Apolarizing plate or a polarizer 5 is attached on the outer surface ofthe lower substrate 100.

On the other hand, an aligning film 6 made of polyimide is coated on theinner surface of an upper substrate 200, which is opposite the lowersubstrate 100 and also made of a transparent insulating material. Apolarizing plate or an analyzer 7 is attached on the outer surface ofthe upper substrate 200.

Finally, a liquid crystal layer 500 having optical anisotropy isinterposed between the aligning films 4 and 6 on the substrates 100 and200.

The light source for the liquid crystal display may be either abacklight unit (not shown) located under the lower substrate 100 or anexternal, natural light which may enter into the LCD through the uppersubstrate 200. In case of reflective type LCD using the natural light,the polarizing plate 5 attached on the lower substrate 100 may not berequired, and it is preferable that the linear electrodes 1 and theplanar electrode 2 are made of opaque material having high reflectancesuch as Aluminum Al. In addition, the lower substrate 100 may be opaque.

A schematic shape of the electric fields of the above-described LCD isdescribed with reference to FIG. 2.

When voltages are applied to the electrodes 1 and 2, the electric fieldshown in FIG. 2 due to the potential difference between the electrodes 1and 2 is generated. In FIG. 2, solid lines indicate equipotential lines,and dotted lines indicate the lines of electrical force.

As shown in FIG. 2, the shape of the electrical field is symmetricalwith respect to a longitudinal central line C (actually the line Ccorresponds to a plane) of a narrow region NR on the linear electrodes 1and a longitudinal central line B (actually the line B also correspondsto a plane) of a wide region WR between the linear electrodes 1. Theline of force has a semi-elliptical or parabolic shape (hereinafter, theshape of the line of force is referred as a semi-elliptical shape forsimplicity) and is generated in a region between the central line C ofthe narrow region NR and the central line B of the wide region WR. Thevertices of the line of force are in a boundary line A (actually theline A corresponds to a surface) between the narrow region NR and thewide region WR.

A tangent of the line of force on the boundary line A between the narrowregion NR and the wide region WR is substantially parallel to thesubstrate 100, and that at central points of the narrow region NR and awide region WR is substantially perpendicular to the substrates 100 and200. In addition, the center and the vertical vertex of the ellipse arepositioned on the boundary line A between the narrow NR and the wideregion WR, and two horizontal vertices are positioned in the wide regionWR and the narrow region NR respectively. The ellipse is asymmetricalwith respect to the boundary line A since the horizontal vertexpositioned in the narrow region NR is closer to the center of theellipse than the horizontal vertex positioned in the wide region WR. Inaddition, the density of the lines of force varies dependent on theposition, and thus the field strength also varies in proportion to thedensity of the lines of force. Accordingly, the field strength is thelargest on the boundary line A—A between the narrow region NR and thewide region WR, and it becomes small as goes to the central lines C—Cand B—B of the broad and the narrow regions BR and NR and to the uppersubstrate 200.

The behaviors of the liquid crystal molecules due to the electric fieldare described hereinafter.

First the initial states of the liquid crystal molecules are described

The two aligning films 4 and 6 are rubbed or exposed to ultravioletlight, and the liquid crystal molecules are aligned in one horizontaldirection. The liquid crystal molecules may have some pre-tilt anglewith respect to the substrates 100 and 200 but they are alignedsubstantially parallel to the substrates 100 and 200. When viewed on aplane parallel to the substrates 100 and 200, the liquid crystalmolecules are arranged to have a predetermined angle with respect to thedirections parallel and perpendicular to the linear electrodes 1. Thepolarizing directions of the polarizing plates 20 and 21 areperpendicular to each other, and the polarizing direction of thepolarizer 5 almost coincides with the rubbing direction. The liquidcrystal material inserted between the two aligning films 4 and 6 is anematic liquid crystal having positive dielectric anisotropy.

It is assumed that the voltages are applied to the linear electrodes 1and the planar electrode 2 and the voltage applied to the linearelectrodes 1 is higher than that to the planar electrode 2. Then, theliquid crystal molecules are re-arranged such that the force due to theelectric field, which depends on the direction and the strength of theelectric field, and an elastical restoring force due to the aligningtreatment are balanced with each other.

The rearrangement of the liquid crystal molecules due to the electricfield is described in detail.

For simplicity, it is assumed that a direction perpendicular to thesubstrates is z direction, a direction perpendicular to the substratesand to the direction of the linear electrodes 1 is x direction, and adirection parallel to the direction of the linear electrodes 1 is ydirection. That is to say, it is assumed that the direction from left toright in FIG. 1 is the positive x direction, the direction upward alongthe linear electrodes 1 in FIG. 1 is the positive y direction, and thedirection from the lower substrate 200 to the upper substrate 100 inFIG. 2 is the positive z direction.

First, the variation of a twist angle, which is defined by the anglemade by the projection of the long axis of the liquid crystal moleculewith the x axis or the initially aligned direction onto xy planeparallel to the substrate 100 and 11, is described with reference toFIGS. 3, 4 and 5.

As shown in FIG. 3, the rubbing direction is indicated by {right arrowover (R)}, an x-y plane component of the electric field is indicated by{right arrow over (E_(xy))}, and the polarizing direction or the opticalaxis of the polarizer 5 is indicated by {right arrow over (P)}, whilethe angle made by the rubbing direction {right arrow over (R)} with thex axis is represented by Ψ_(R), and the angle made by the long axis ofthe liquid crystal molecule with the x axis is represented by Ψ_(LC).The angle Ψ_(P) made by the optical axis of the polarizer 5 with thex-axis is equal to Ψ_(R) since the optical axis of the polarizer 5 isparallel to the rubbing direction {right arrow over (R)}.

The x-y plane component {right arrow over (E_(xy))} of the electricfield is in the positive x direction from the boundary line A to thecentral line B of the wide region WR, and in the negative x directionfrom the central line B of the wide region WR to the next boundary lineD.

The strength of the electric field component {right arrow over (E_(xy))}is the largest on the boundary lines A and D, and it becomes smaller asgoes to the central line B—B, where the strength of the electric fieldcomponent {right arrow over (E_(xy))} is zero.

The magnitude of the elastical restoring force generated by the rubbingprocess is substantially constant on the xy plane regardless ofposition.

As illustrated in FIG. 4, the long axis of the liquid crystal moleculeor the molecular axis on the boundary lines A and D is substantiallyparallel to the electric field component {right arrow over (E_(xy))},and makes a large angle with respect to the rubbing direction {rightarrow over (R)} since the liquid crystal molecules may be arranged tobalance the two forces. However, the closer to the central lines C and Bof the regions NR and WR, the smaller the angle |Ψ_(R)-Ψ_(LC)| which themolecular axis makes with the rubbing direction {right arrow over (R)},and the molecular axis on the central lines B and C is in the rubbingdirection {right arrow over (R)}. The angle made by the optical axis ofthe polarizer 5 with the molecular axis has the same distribution as theabove since the optical axis of the polarizer 5 is parallel to therubbing direction {right arrow over (R)}, and this angle is closelyrelated to the transmittance of the incident light.

Various shapes of electric fields may be generated by varying the ratioof the widths of the narrow region NR and the wide region WR. Althoughthe narrow region NR on the linear electrodes 1 cannot be used as thedisplay region when the linear electrodes 1 are opaque, it may be alsoused as the display region when the linear electrodes 1 are transparent.

On the other hand, the xy plane component of the electric field {rightarrow over (E_(xy))} becomes smaller along the z-axis as goes from thelower aligning film 4 to the upper aligning film 6. The elasticrestoring force generated by the aligning treatment is the greatest onthe surfaces of the aligning films 4 and 6, and it is reduced as goes tothe center of the liquid crystal layer between the aligning films 4 and6.

FIG. 5 illustrates the twist angle made by the molecular axis with thex-axis from the lower aligning film 4 to the upper aligning film 6 alongthe z-axis. In FIG. 5, the horizontal axis indicates the height from thelower aligning film 4, and the vertical axis represents the twist angle,where d is the cell gap between the two aligning films 4 and 6.

As illustrated in FIG. 5, the twist angle on the surfaces of thealigning films 4 and 6 is large since the aligning force of the aligningfilms 4 and 6 is great. The twist angle becomes small as goes to thecenter of the liquid crystal layer, and the molecular axis at the centerof the liquid crystal layer is substantially in the direction of theelectric field component {right arrow over (E_(xy))}. The molecular axisjust on the aligning films 4 and 6 is arranged in the rubbing direction{right arrow over (R)}.

Supposing that the difference of the twist angle between the adjacentliquid crystal molecules is called twist, the twist corresponds to theslope of the curve in FIG. 5. The twist is large near the surfaces ofthe aligning films 4 and 6, and it decreases as goes to the center ofthe liquid crystal layer.

FIGS. 6, 7 and 8 illustrate the variation of the tilt angle which themolecular axis makes with x-axis or the initially aligned direction on aplane perpendicular to the substrate, for example, zx plane. FIG. 6illustrates only the substrates 100 and 200 for the purpose ofsimplifying explanation. In FIG. 6, the zx plane component of the {rightarrow over (R)} indicating the rubbing direction in FIG. 3 isrepresented by {right arrow over (R_(zx))}, and the zx plane componentof the electric field is represented by {right arrow over (E_(zx))},while the angle made by the field component {right arrow over (E_(zx))}with the x axis is indicated by θ_(E), and the tilt angle made by themolecular axis with the x axis is indicated by θ_(LC). Here, {rightarrow over (R_(zx))} is in the x direction since the vector {right arrowover (R)} exists on the xy plane assuming a pretilt angle is ignored.

The magnitude of the field component {right arrow over (E_(zx))} and theangle θ_(E) becomes small as goes to the upper substrate 200 from thelower substrate 100.

As described above, the elastic restoring force by the aligningtreatment is the largest on the surfaces of the two substrates 100 and200, and it becomes small as goes to the center of the liquid crystallayer.

The liquid crystal molecules may be arranged to balance the two forces.As illustrated in FIG. 7, the molecular axis on the surfaces of thesubstrates 100 and 200 is arranged substantially parallel to the x-axissince the aligning force is the strongest there. Since the force due tothe electric field becomes relatively stronger compared with thealigning force from the substrates 100 and 200 to a certain point, themagnitude of the tilt angle θ_(LC) increases continuously. Here, thevertex of the curve is formed at a point near the lower substrate 100.

On the other hand, the angle θ_(E) which the field component {rightarrow over (E_(zx))} makes with the x axis is almost zero on theboundary lines A and D, and it becomes large as goes to the central lineB—B. The magnitude of the field component {right arrow over (E_(zx))} isthe greatest on the boundary lines A and D, and it is reduced as goes tothe central line B—B.

The magnitude of the elastic restoring force by the aligning treatmentis constant on the x axis regardless of the position.

Accordingly, as illustrated in FIG. 8, the tilt angle of the liquidcrystal molecule is almost zero on the boundary lines A and D, and itdecreases as goes to the central lines C and B. Therefore, the tiltangle of the liquid crystal molecules has the similar distributions tothe angle θ_(E) made by the field component {right arrow over (E_(zx))}with the x axis, although the tilt angle varies more smoothly than theangle θ_(E).

As described above, when the voltages are applied to the two electrodes1 and 2, the liquid crystal molecules are re-arranged to have the twistangle and the tilt angle. The transmittance of the incident light varydue to the variation of the twist angle and the tilt angle. On theboundary lines A and D, there is little variation in the tilt anglealong the z axis, but the twist angle varies very much. On the centrallines B and C, on the other hand, there is little variation in the twistangle along the z axis but there is a little variation in the tiltangle. Accordingly, both the twist angle and the tilt angle varies inthe region between the boundary lines A and D and the central lines Band C. As a result, a transmittance curve as a function of position hasa similar shape to the lines of force.

The transmittance and the viewing angle characteristics of the LCDaccording to the first embodiment of the present invention are describedwith reference to experimental results illustrated in FIGS. 9, 10 and11.

In the experiment, the linear electrodes 1 was made the opaque material,the widths of the narrow and the wide regions NR was 5 μm and 17 μmrespectively, the voltage applied to the planar and the linearelectrodes 2 and 1 was 0 V and 5 V respectively, Ψ_(R) was 80°, thepre-tilt angle was about 1.5°, and the cell gap was 4.5 μm.

FIG. 9 is a graphical illustration of the transmittance as a function ofposition along the x-axis according to the experiment, where the originis located at the left boundary line of the leftest linear electrode 1in FIG. 3.

As illustrated in FIG. 9, the transmittance is zero in the opaque narrowregion NR, has minima near the central lines B of the wide region WR,and has maxima in the central region between the boundary lines A and Dand the central lines B.

FIG. 10 illustrates the transmittance as a function of the appliedvoltage according the experiment, where the horizontal axis indicatesthe applied voltage, and the vertical axis indicates the transmittance.As shown in FIG. 10, the threshold voltage is about 1.5 V, and thesaturation voltage is about 3 V. Accordingly, it is possible to drivethe LCD of the present invention with the low voltage less than 3V.

FIG. 11 is a graphical illustration showing the viewing anglecharacteristics according to the experiment. As shown in FIG. 11, theboundary of the region where the contrast is equal to or more than 10 issubstantially over 60 degrees.

When using optical phase compensating films between the polarizingplates and the substrates, the viewing angle may become wider.

In the above-mentioned embodiment and experiments, it is possible tomodify the kind of the liquid crystal material, the kind of the aligningfilms, aligning methods, the pre-tilt angle, the polarizing directionsof the polarizing plates, the cell gaps, the kind of the phasedifference compensating plates, the material forming the electrodes, thewidths of the electrodes and the distances between the electrodes. Forexample, when the linear electrodes 1 are made of the transparentmaterial, the higher transmittance can be obtained since the liquidcrystal molecules on the linear electrodes 1 are used for controllingthe light.

The modifications of the kind of the liquid crystal and/or of initialstate are described through second to fourth embodiments.

The second embodiment uses a liquid crystal having negative dielectricanisotropy.

The structure of an LCD according to the second embodiment is similar tothe first embodiment, and thus the shape of the electric field issimilar. However, the rearrangement of the liquid crystal molecules dueto the electric field is different from the first embodiment.

In the initial state, the two aligning films 4 and 6 are rubbed orexposed to ultraviolet light, and the liquid crystal molecules arealigned in one horizontal direction. The liquid crystal molecules mayhave some pre-tilt angle of less than 7 degrees with respect to thesubstrates 100 and 200 but they are aligned substantially parallel tothe substrates 100 and 200. When viewed on a plane parallel to thesubstrates 100 and 200, the liquid crystal molecules are arranged tohave a predetermined angle of equal to or less than 45 degrees withrespect to the directions parallel and perpendicular to the linearelectrodes 1. The polarizing directions of the polarizing plates 20 and21 are perpendicular to each other, and the polarizing direction of thepolarizer 5 almost coincides with the rubbing direction. Then theinitial state is black state.

For simplicity, it is assumed that a direction perpendicular to thesubstrates is z direction, a direction perpendicular to the substratesand to the direction of the linear electrodes 1 is x direction, and adirection parallel to the direction of the linear electrodes 1 is ydirection. That is to say, it is assumed that the direction from left toright in FIG. 1 is the positive x direction, the direction upward alongthe linear electrodes 1 in FIG. 1 is the positive y direction, and thedirection from the lower substrate 200 to the upper substrate 100 inFIG. 2 is the positive z direction.

First, the variation of a twist angle, which is defined by the anglemade by the projection of the long axis of the liquid crystal moleculewith the x axis or the initially aligned direction onto xy-planeparallel to the substrate 100 and 11, is described with reference toFIGS. 12, 13 and 14.

As shown in FIG. 12, the rubbing direction is indicated by {right arrowover (R)}, an x-y plane component of the electric field is indicated by{right arrow over (E_(xy))}, and the polarizing direction or the opticalaxis of the polarizer 5 is indicated by {right arrow over (P)}, whilethe angle made by the rubbing direction {right arrow over (R)} with thex axis is represented by ψ_(R), and the angle made by the long axis ofthe liquid crystal molecule with the x axis is represented by ψ_(LC).The angle ψ_(P) made by the optical axis of the polarizer 5 with thex-axis is equal to ψ_(R) since the optical axis of the polarizer 5 isparallel to the rubbing direction {right arrow over (R)}.

The x-y plane component {right arrow over (E_(xy))} of the electricfield is in the positive x direction from the boundary line A to thecentral line B of the wide region WR, and in the negative x directionfrom the central line B of the wide region WR to the next boundary lineD.

The strength of the electric field component {right arrow over (E_(xy))}is the largest on the boundary lines A and D, and it becomes smaller asgoes to the central line B—B, where the strength of the electric fieldcomponent {right arrow over (E_(xy))} is zero.

The magnitude of the elastically restoring force generated by therubbing process is substantially constant on the xy plane regardless ofposition.

As illustrated in FIG. 13, the long axis of the liquid crystal moleculeor the molecular axis on the boundary lines A and D is substantiallyperpendicular to the electric field component {right arrow over(E_(xy))}, and to the rubbing direction {right arrow over (R)} since theliquid crystal molecules may be arranged to balance the two forces.However, the closer to the central lines C and B of the regions NR andWR, the smaller the angle |ψ_(R)−ψ_(LC)| which the molecular axis makeswith the rubbing direction {right arrow over (R)}, and the molecularaxis on the central lines B and C is in the rubbing direction {rightarrow over (R)}. The angle made by the optical axis of the polarizer 5with the molecular axis has the same distribution as the above since theoptical axis of the polarizer 5 is parallel to the rubbing direction{right arrow over (R)}, and this angle is closely related to thetransmittance of the incident light.

On the other hand, the xy plane component of the electric field {rightarrow over (R_(xy))} becomes smaller along the z-axis as goes from thelower aligning film 4 to the upper aligning film 6. The elasticrestoring force generated by the aligning treatment is the greatest onthe surfaces of the aligning films 4 and 6, and it is reduced as goes tothe center of the liquid crystal layer between the aligning films 4 and6.

FIG. 14 illustrates the twist angle made by the molecular axis with thex-axis from the lower aligning film 4 to the upper aligning film 6 alongthe z-axis. In FIG. 14, the horizontal axis indicates the height fromthe lower aligning film 4, and the vertical axis represents the twistangle, where d is the cell gap between the two aligning films 4 and 6.

As illustrated in FIG. 14, the twist angle on the surfaces of thealigning films 4 and 6 is large since the aligning force of the aligningfilms 4 and 6 is great. The twist angle becomes small as goes to thecenter of the liquid crystal layer, and the molecular axis at the centerof the liquid crystal layer is substantially in the direction of theelectric field component {right arrow over (E_(xy))}. The molecular axisjust on the aligning films 4 and 6 is arranged in the rubbing direction{right arrow over (R)}.

Supposing that the difference of the twist angle between the adjacentliquid crystal molecules is called twist, the twist corresponds to theslope of the curve in FIG. 14. The twist is large near the surfaces ofthe aligning films 4 and 6, and it decreases as goes to the center ofthe liquid crystal layer.

FIGS. 15, 16 and 17 illustrate the variation of the tilt angle which themolecular axis makes with x-axis or the initially aligned direction on aplane perpendicular to the substrate, for example, zx-plane. FIG. 15illustrates only the substrates 100 and 200 for the purpose ofsimplifying explanation. In FIG. 15, the zx plane component of the{right arrow over (R)} indicating the rubbing direction in FIG. 12 isrepresented by {right arrow over (R_(zx))}, and the zx plane componentof the electric field is represented by {right arrow over (E_(zx))},while the angle made by the field component {right arrow over (E_(zx))}with the x axis is indicated by θ_(E), and the tilt angle made by themolecular axis with the x axis is indicated by θ_(LC). Here, {rightarrow over (R_(zx))} is in the x direction since the vector {right arrowover (R)} exists on the xy plane assuming a pretilt angle is ignored.

The magnitude of the field component {right arrow over (E_(zx))} and theangle θ_(E) becomes small as goes to the upper substrate 200 from thelower substrate 100.

As described above, the elastic restoring force by the aligningtreatment is the largest on the surfaces of the two substrates 100 and200, and it becomes small as goes to the center of the liquid crystallayer.

The liquid crystal molecules may be arranged to balance the two forces.As illustrated in FIG. 7, the molecular axis on the surfaces of thesubstrates 100 and 200 is arranged substantially parallel to the x-axissince the aligning force is the strongest there. Since the force due tothe electric field becomes relatively stronger compared with thealigning force from the substrates 100 and 200 to a certain point, themagnitude of the tilt angle θ_(LC) increases continuously. Here, thevertex of the curve is formed at a point near the lower substrate 100.

On the other hand, the angle θ_(E) which the field component {rightarrow over (E_(zx))} makes with the x axis is almost zero on theboundary lines A and D, and it becomes large as goes to the central lineB—B. The magnitude of the field component {right arrow over (E_(zx))} isthe greatest on the boundary lines A and D, and it is reduced as goes tothe central line B—B.

The magnitude of the elastic restoring force by the aligning treatmentis constant on the x-axis regardless of the position.

Accordingly, as illustrated in FIG. 17, the tilt angle of the liquidcrystal molecule is almost zero on the boundary lines A and D, and itdecreases as goes to the central lines C and B. Therefore, the tiltangle of the liquid crystal molecules has the similar distributions tothe angle θ_(E) made by the field component {right arrow over (E_(zx))}with the x axis, although the tilt angle varies more smoothly than theangle θ_(E).

As described above, when the voltages are applied to the two electrodes1 and 2, the liquid crystal molecules are re-arranged to have the twistangle and the tilt angle. The transmittance of the incident light variesdue to the variation of the twist angle and the tilt angle. On theboundary lines A and D, there is little variation in the tilt anglealong the z-axis, but the twist angle varies very much. On the centrallines B and C, on the other hand, there is little variation in the twistangle along the z-axis but there is a little variation in the tiltangle. Accordingly, both the twist angle and the tilt angle vary in theregion between the boundary lines A and D and the central lines B and C.As a result, a transmittance curve as a function of position has asimilar shape to the lines of force.

The third embodiment uses a liquid crystal having positive dielectricanisotropy but the liquid crystal molecules it their initial states areperpendicular to the substrates.

The structure of an LCD according to the third embodiment is similar tothe first embodiment, and thus the shape of the electric field issimilar. However, the rearrangement of the liquid crystal molecules dueto the different initial states is different from the first embodiment.

In the initial state, the two aligning films 4 and 6 are rubbed orexposed to ultraviolet light, and the liquid crystal molecules arealigned perpendicular to the substrates 100 and 200. The liquid crystalmolecules may have some pre-tilt angle with respect to the substrates100 and 200 but they are aligned substantially perpendicular to thesubstrates 100 and 200. When viewed on a plane parallel to thesubstrates 100 and 200, the liquid crystal molecules are arranged tohave a predetermined angle with respect to the directions parallel andperpendicular to the linear electrodes 1. The polarizing directions ofthe polarizing plates 20 and 21 are perpendicular to each other, and thepolarizing direction of the polarizer 5 almost coincides with therubbing direction. Then the initial state is black state. The liquidcrystal is nematic and may have chiral dopant of 0.001-3.0 wt %.

For simplicity, it is assumed that a direction perpendicular to thesubstrates is z direction, a direction perpendicular to the substratesand to the direction of the linear electrodes 1 is x direction, and adirection parallel to the direction of the linear electrodes 1 is ydirection. That is to say, it is assumed that the direction from left toright in FIG. 1 is the positive x direction, the direction upward alongthe linear electrodes 1 in FIG. 1 is the positive y direction, and thedirection from the lower substrate 200 to the upper substrate 100 inFIG. 2 is the positive z direction.

First, the variation of a twist angle, which is defined by the anglemade by the projection of the long axis of the liquid crystal moleculewith the x axis or the initially aligned direction onto xy planeparallel to the substrate 100 and 11, is described with reference toFIGS. 18, 19 and 20.

As shown in FIG. 18, the rubbing direction is indicated by {right arrowover (R)}, an x-y plane component of the electric field is indicated by{right arrow over (E_(xy))}, and the polarizing direction or the opticalaxis of the polarizer 5 is indicated by {right arrow over (P)}, whilethe angle made by the rubbing direction {right arrow over (R)} with thex axis is represented by ψ_(R), and the angle made by the long axis ofthe liquid crystal molecule with the x axis is represented by ψ_(LC).The angle ψ_(P) made by the optical axis of the polarizer 5 with thex-axis is equal to ψ_(R) since the optical axis of the polarizer 5 isparallel to the rubbing direction {right arrow over (R)}.

The x-y plane component {right arrow over (E_(xy))} of the electricfield is in the positive x direction from the boundary line A to thecentral line B of the wide region WR, and in the negative x directionfrom the central line B of the wide region WR to the next boundary lineD.

The strength of the electric field component {right arrow over (E_(xy))}is the largest on the boundary lines A and D, and it becomes smaller asgoes to the central line B—B, where the strength of the electric fieldcomponent {right arrow over (E_(xy))} is zero.

The magnitude of the elastically restoring force generated by therubbing process is substantially constant on the xy plane regardless ofposition.

As illustrated in FIG. 19, the long axis of the liquid crystal moleculeor the molecular axis on the boundary lines A and D is substantiallyparallel to the electric field component {right arrow over (E_(xy))},and makes a large angle with respect to the rubbing direction {rightarrow over (R)} since the liquid crystal molecules may be arranged tobalance the two forces. However, the closer to the central lines C and Bof the regions NR and WR, the smaller the angle |ψ_(R). . . ψ_(LC)|which the molecular axis makes with the rubbing direction {right arrowover (R)}, and the molecular axis on the central lines B and C is in therubbing direction {right arrow over (R)}. The angle made by the opticalaxis of the polarizer 5 with the molecular axis has the samedistribution as the above since the optical axis of the polarizer 5 isparallel to the rubbing direction {right arrow over (R)}, and this angleis closely related to the transmittance of the incident light.

On the other hand, the xy plane component of the electric field {rightarrow over (R_(xy))} becomes smaller along the z-axis as goes from thelower aligning film 4 to the upper aligning film 6. The elasticrestoring force generated by the aligning treatment is the greatest onthe surfaces of the aligning films 4 and 6, and it is reduced as goes tothe center of the liquid crystal layer between the aligning films 4 and6.

FIG. 20 illustrates the twist angle made by the molecular axis with thex-axis from the lower aligning film 4 to the upper aligning film 6 alongthe z-axis. In FIG. 20, the horizontal axis indicates the height fromthe lower aligning film 4, and the vertical axis represents the twistangle, where d is the cell gap between the two aligning films 4 and 6.

As illustrated in FIG. 20, the twist angle on the surfaces of thealigning films 4 and 6 is large since the aligning force of the aligningfilms 4 and 6 is great. The twist angle becomes small as goes to thecenter of the liquid crystal layer, and the molecular axis at the centerof the liquid crystal layer is substantially in the direction of theelectric field component {right arrow over (E_(xy))}. The molecular axisjust on the aligning films 4 and 6 is arranged in the rubbing direction{right arrow over (R)}.

Supposing that the difference of the twist angle between the adjacentliquid crystal molecules is called twist, the twist corresponds to theslope of the curve in FIG. 20. The twist is large near the surfaces ofthe aligning films 4 and 6, and it decreases as goes to the center ofthe liquid crystal layer.

FIGS. 21, 22 and 23 illustrate the variation of the tilt angle which themolecular axis makes with x-axis or the initially aligned direction on aplane perpendicular to the substrate, for example, zx plane. FIG. 21illustrates only the substrates 100 and 200 for the purpose ofsimplifying explanation. In FIG. 21, the zx plane component of the{right arrow over (R)} indicating the rubbing direction in FIG. 18 isrepresented by {right arrow over (R_(zx))}, and the zx plane componentof the electric field is represented by {right arrow over (E_(zx))},while the angle made by the field component {right arrow over (E_(zx))}with the z axis is indicated by θ_(E), and the tilt angle made by themolecular axis with the z axis is indicated by θ_(LC). Here, {rightarrow over (R_(zx))} is in the x direction since the vector {right arrowover (R)} exists on the xy plane assuming a pretilt angle is ignored.

The magnitude of the field component {right arrow over (E_(zx))} and theangle θ_(E) becomes small as goes to the upper substrate 200 from thelower substrate 100.

As described above, the elastic restoring force by the aligningtreatment is the largest on the surfaces of the two substrates 100 and200, and it becomes small as goes to the center of the liquid crystallayer.

The liquid crystal molecules may be arranged to balance the two forces.As illustrated in FIG. 21 the molecular axis on the surfaces of thesubstrates 100 and 200 is arranged substantially parallel to the z-axissince the aligning force is the strongest there. Since the force due tothe electric field becomes relatively stronger compared with thealigning force from the substrates 100 and 200 to a certain point, themagnitude of the tilt angle θ_(LC) increases continuously. Here, thevertex of the curve is formed at a point near the lower substrate 100.

On the other hand, the angle θ_(E) which the field component {rightarrow over (E_(zx))} makes with the z axis is almost 90 degrees on theboundary lines A and D, and it becomes small as goes to the central lineB—B. The magnitude of the field component {right arrow over (E_(zx))} isthe greatest on the boundary lines A and D, and it is reduced as goes tothe central line B—B.

The magnitude of the elastic restoring force by the aligning treatmentis constant on the x-axis regardless of the position.

Accordingly, as illustrated in FIG. 23, since the long axes of theliquid crystal molecule at the boundary lines A and D are almostperpendicular to the field direction, the lines A and D form adiscontinuous plane. However, the tilt angle of the liquid crystalmolecules is almost 90 degrees near the boundary lines A and D, and itdecreases as goes to the central lines C and B. Therefore, the tiltangle of the liquid crystal molecules has the similar distributions tothe angle θ_(F) made by the field component {right arrow over (E_(zx))}with the z axis, although the tilt angle varies more smoothly than theangle θ_(E).

When the liquid crystal molecules have pre-tilt angle, the discontinuousplane may be eliminated.

As described above, when the voltages are applied to the two electrodes1 and 2, the liquid crystal molecules are re-arranged to have the twistangle and the tilt angle. The transmittance of the incident light variesdue to the variation of the twist angle and the tilt angle. On theboundary lines A and D, there is large variation in the tilt angle andthe twist angle along the z-axis. On the central lines B and C, on theother hand, there is little variation in the twist angle and the tiltangle along the z-axis. Accordingly, both the twist angle and the tiltangle vary in the region between the boundary lines A and D and thecentral lines B and C. As a result, a transmittance curve as a functionof position has a similar shape to the lines of force.

The fourth embodiment uses a liquid crystal having negative dielectricanisotropy and the liquid crystal molecules in their initial states areperpendicular to the substrates.

The structure of an LCD according to the third embodiment is similar tothe first embodiment, and thus the shape of the electric field issimilar. However, the rearrangement of the liquid crystal molecules dueto the different initial states is different from the first embodiment.

In the initial state, the two aligning films 4 and 6 are rubbed orexposed to ultraviolet light, and the liquid crystal molecules arealigned perpendicular to the substrates 100 and 200. The liquid crystalmolecules may have some pre-tilt angle with respect to the substrates100 and 200 but they are aligned substantially parallel to thesubstrates 100 and 200. When viewed on a plane parallel to thesubstrates 100 and 200, the liquid crystal molecules are arranged tohave a predetermined with respect to the directions parallel andperpendicular to the linear electrodes 1. The polarizing directions ofthe polarizing plates 20 and 21 are perpendicular to each other, and thepolarizing direction of the polarizer 5 almost coincides with therubbing direction. Then the initial state is black state. The liquidcrystal is nematic and may have chiral dopant of 0.001-3.0 wt %.

For simplicity, it is assumed that a direction perpendicular to thesubstrates is z direction, a direction perpendicular to the substratesand to the direction of the linear electrodes 1 is x direction, and adirection parallel to the direction of the linear electrodes 1 is ydirection. That is to say, it is assumed that the direction from left toright in FIG. 1 is the positive x direction, the direction upward alongthe linear electrodes 1 in FIG. 1 is the positive y direction, and thedirection from the lower substrate 200 to the upper substrate 100 inFIG. 2 is the positive z direction.

First, the variation of a twist angle, which is defined by the anglemade by the projection of the long axis of the liquid crystal moleculewith the x axis or the initially aligned direction onto xy planeparallel to the substrate 100 and 11, is described with reference toFIGS. 24, 25 and 26.

As shown in FIG. 24, the rubbing direction is indicated by {right arrowover (R)}, an x-y plane component of the electric field is indicated by{right arrow over (E_(xy))}, and the polarizing direction or the opticalaxis of the polarizer 5 is indicated by {right arrow over (P)}, whilethe angle made by the rubbing direction {right arrow over (R)} with thex axis is represented by ψ_(R), and the angle made by the long axis ofthe liquid crystal molecule with the x axis is represented by ψ_(LC).The angle ψ_(P) made by the optical axis of the polarizer 5 with thex-axis is equal to ψ_(R) since the optical axis of the polarizer 5 isparallel to the rubbing direction {right arrow over (R)}.

The x-y plane component {right arrow over (E_(xy))} of the electricfield is in the positive x direction from the boundary line A to thecentral line B of the wide region WR, and in the negative x directionfrom the central line B of the wide region WR to the next boundary lineD.

The strength of the electric field component {right arrow over (E_(xy))}is the largest on the boundary lines A and D, and it becomes smaller asgoes to the central line B—B, where the strength of the electric fieldcomponent {right arrow over (E_(xy))} is zero.

The magnitude of the elastically restoring force generated by therubbing process is substantially constant on the xy plane regardless ofposition.

As illustrated in FIG. 25, the long axis of the liquid crystal moleculeor the molecular axis on the boundary lines A and D is substantiallyperpendicular to the electric field component {right arrow over(E_(xy))}, and to the rubbing direction {right arrow over (R)} since theliquid crystal molecules may be arranged to balance the two forces.However, the closer to the central lines C and B of the regions NR andWR, the smaller the angle |ψ_(R)-ψ_(LC)| which the molecular axis makeswith the rubbing direction {right arrow over (R)}, and the molecularaxis on the central lines B and C is in the rubbing direction {dot over(R)}. The angle made by the optical axis of the polarizer 5 with themolecular axis has the same distribution as the above since the opticalaxis of the polarizer 5 is parallel to the rubbing direction {rightarrow over (R)}, and this angle is closely related to the transmittanceof the incident light.

On the other hand, the xy plane component of the electric field {rightarrow over (R_(xy))} becomes smaller along the z-axis as goes from thelower aligning film 4 to the upper aligning film 6. The elasticrestoring force generated by the aligning treatment is the greatest onthe surfaces of the aligning films 4 and 6, and it is reduced as goes tothe center of the liquid crystal layer between the aligning films 4 and6.

FIG. 26 illustrates the twist angle made by the molecular axis with thex-axis from the lower aligning film 4 to the upper aligning film 6 alongthe z-axis. In FIG. 26, the horizontal axis indicates the height fromthe lower aligning film 4, and the vertical axis represents the twistangle, where d is the cell gap between the two aligning films 4 and 6.

As illustrated in FIG. 26, the twist angle on the surfaces of thealigning films 4 and 6 is large since the aligning force of the aligningfilms 4 and 6 is great. The twist angle becomes small as goes to thecenter of the liquid crystal layer, and the molecular axis at the centerof the liquid crystal layer is substantially in the direction of theelectric field component {right arrow over (E_(xy))}. The molecular axisjust on the aligning films 4 and 6 is arranged in the rubbing direction{right arrow over (R)}.

Supposing that the difference of the twist angle between the adjacentliquid crystal molecules is called twist, the twist corresponds to theslope of the curve in FIG. 26. The twist is large near the surfaces ofthe aligning films 4 and 6, and it decreases as goes to the center ofthe liquid crystal layer.

FIGS. 27, 28 and 29 illustrate the variation of the tilt angle which themolecular axis makes with x-axis or the initially aligned direction on aplane perpendicular to the substrate, for example, zx plane. FIG. 27illustrates only the substrates 100 and 200 for the purpose ofsimplifying explanation. In FIG. 27, the zx plane component of the{right arrow over (R)} indicating the rubbing direction in FIG. 24 isrepresented by {right arrow over (R_(zx))}, and the zx plane componentof the electric field is represented by {right arrow over (E_(zx))},while the angle made by the field component {right arrow over (E_(zx))}with the z axis is indicated by θ_(E), and the tilt angle made by themolecular axis with the z axis is indicated by θ_(LC). Here, {rightarrow over (R_(zx))} is in the x direction since the vector {right arrowover (R)} exists on the xy plane assuming a pretilt angle is ignored.

The magnitude of the field component {right arrow over (E_(zx))} and theangle θ_(E) becomes small as goes to the upper substrate 200 from thelower substrate 100.

As described above, the elastic restoring force by the aligningtreatment is the largest on the surfaces of the two substrates 100 and200, and it becomes small as goes to the center of the liquid crystallayer.

The liquid crystal molecules may be arranged to balance the two forces.As illustrated in FIG. 27, the molecular axis on the surfaces of thesubstrates 100 and 200 is arranged substantially parallel to the z-axissince the aligning force is the strongest there. Since the force due tothe electric field becomes relatively stronger compared with thealigning force from the substrates 100 and 200 to a certain point, themagnitude of the tilt angle θ_(LC) increases continuously. Here, thevertex of the curve is formed at a point near the lower substrate 100.

On the other hand, the angle θ_(E) which the field component {rightarrow over (E_(zx))} makes with the z axis is almost 90 degrees on theboundary lines A and D, and it becomes small as goes to the central lineB—B. The magnitude of the field component {right arrow over (E_(zx))} isthe greatest on the boundary lines A and D, and it is reduced as goes tothe central line B—B.

The magnitude of the elastic restoring force by the aligning treatmentis constant on the x-axis regardless of the position.

Accordingly, as illustrated in FIG. 29, the tilt angle of the liquidcrystal molecule is almost zero degrees on the boundary lines A and D,and it increases as goes to the central lines C and B. Therefore, thetilt angle of the liquid crystal molecules has the similar distributionsto the angle θ_(E) made by the field component {right arrow over(E_(zx))} with the z axis, although the tilt angle varies more smoothlythan the angle θ_(E).

When the liquid crystal molecules have pre-tilt angle, the discontinuousplane may be eliminated.

As described above, when the voltages are applied to the two electrodes1 and 2, the liquid crystal molecules are re-arranged to have the twistangle and the tilt angle. The transmittance of the incident light variesdue to the variation of the twist angle and the tilt angle. On theboundary lines A and D, there is little variation in the tilt angle butthe twist angle along the z-axis varies greatly. On the central lines Band C, on the other hand, there is little variation in the twist anglealong the z-axis but there is a little variation in the tilt angle.Accordingly, both the twist angle and the tilt angle vary in the regionbetween the boundary lines A and D and the central lines B and C. As aresult, a transmittance curve as a function of position has a similarshape to the lines of force.

Next, modifications of the structure of the electrodes are described.

The LCD according to the fifth embodiment of the present invention isdescribed with reference to the FIGS. 30 and 31.

Unlike the first to fourth embodiments of the present invention, theportions of the planar electrode overlapping the linear electrodes areremoved in this embodiment. Therefore, the planar electrode is dividedinto a plurality of common electrodes 200, each being located betweenthe linear electrodes 1. Furthermore, since the two adjacent commonelectrodes 20 in the transverse direction should be connected, there areprovided common electrode lines or connections 23 connecting the commonelectrodes 200. These connections 23 may overlap the linear electrodes 1as shown in FIG. 30, but may be located outward the linear electrodes 1in order to preventing overlapping. In FIG. 30, openings 8 are definedby the adjacent two common electrodes 20 and the connections 23connecting them.

For simplicity, a region on a linear electrode 1 is defined as a narrowregion NR, a region including an opening 8 and connections 23 as aboundary region BR, and a region on the common electrode 20 as a wideregion WR, while the widths of the narrow region NR, the boundary regionBR, and the wide region WR is designated as a, c and b, respectively.

In FIG. 31 which is a cross-section view taken along line V-V′ in FIG.30, the lines of force between the central line C of the narrow regionNR and the central line B of the wide region WR are in parabolic orsemi-elliptical shapes. When the width of the boundary region BR isfixed, the location of the vertex of the line of force varies dependingon the value of the a/b. However, the vertex of the parabolic line offorce is located approximately on the central line I of the boundaryregion BR. The shape of the parabola is asymmetric when a is differentfrom b, but is substantially symmetric when a and b are the same. When cis zero, the electric field has the shape similar to the electric fieldof the first embodiment, and even though c is not zero, the electricfield on the planar electrode 2 or the linear electrodes 1 also has thehorizontal component and the vertical component.

Accordingly, in the transmissive type display where both or either ofthe two electrodes 1 and 2 is made of transparent material, the lightincident on the liquid crystal layer through the transparent electrode 1or 2 is controlled by the twist and the tilt of the liquid crystalmolecules on the transparent electrode. Here, the smaller the value ofc, the lesser the threshold voltage of the liquid crystal material.

In case of the reflection type display where the two electrodes 1 and 2are made of opaque metal having high reflectance such as Al, thereflectance is high as the value of c is small. In this case, there-arranged liquid crystal molecules on the electrodes 1 and 2 havingthe twist angle and the tilt angle change the polarization of the lightincident on the liquid crystal layer through the upper substrate andthat of the light which is reflected by the electrodes 1 and 2 andincident on the liquid crystal layer.

The LCD according to the sixth embodiment of the present inventionhaving a thin film transistor as a switching element as well as theelectrodes suggested in the first to the fifth embodiments, is describedin detail with reference to FIGS. 32 to 34.

FIG. 32 is a layout of a pixel formed on the lower substrate of the LCDaccording to the sixth embodiment of the present invention, whereinhundreds of thousands of such pixels are formed in a matrix type in theLCD.

A plurality of gate lines or scanning signal lines 10 and a plurality ofplanar common electrodes 20 are formed on a transparent insulatingsubstrate 100. The scanning signal lines 10 are elongated in thetransverse direction, and the common electrodes are located between thescanning signal lines 10. A portion 11 of the scanning signal line 10serve as a gate electrode, and connections 23 connect adjacent commonelectrodes 20.

The scanning signal lines 10 and the common electrodes 20 are coveredwith a gate insulating film 40, and a channel layer 51 made of amorphoussilicon is formed on a portion of a gate insulating film 40 opposite thegate electrode 11 of the scanning signal line 10. Two separated portions61 and 62 of the doped amorphous silicon layer heavily doped with n-typeimpurity are formed on portions of the channel layer 51, and theportions 61 and 62 are opposite each other with respect to the gateelectrode 11.

On the other hand, a plurality of data lines 70 are formed on the gateinsulating film 40 and elongated longitudinally to intersect the gatelines 10. A branch of the data line 70 extends to one portion 61 of thedoped amorphous silicon layer to form a source electrode 71, and a drainelectrode 72 is formed on the other portion 62 of the doped amorphoussilicon layer. The gate electrode 11, the source electrode 71 and thedrain electrode 72 form electrodes of the TFT along with the channellayer 51. The doped amorphous silicon layer 61 and 62 improves ohmiccontact between the source and the drain electrodes 71 and 72 and theamorphous silicon layer 51.

The drain electrode 72 extends to form a plurality of linear pixelelectrodes 75 elongated longitudinally and a connecting portion 76 ofthe pixel electrodes 75. The data line 70, the source and the drainelectrodes 71 and 72 and the connecting portion 76 are covered with apassivation film 80, and the aligning film 4 is coated thereon.

Since the connections 23 overlap the data line 70, and the overlappingcauses parasitic capacitance to increase the RC delay of the imagesignal of the data line 70. To reduce the RC delay, it is preferablethat the overlapping between the connection 23 and the data line 70 isminimized.

A portion of the passivation film 80 in the display region where thepixel electrode 75 and the common electrode 20 are located may beremoved to obtain sufficient electric field.

Other amorphous silicon patterns 52 are formed on the portions of thegate insulating layer 3 where the gate lines 10, the connections 23intersect the data lines 70 in order to enhance the insulationtherebetween.

A method for manufacturing the LCD according to the sixth embodiment ofthe present invention is described in detail hereinafter.

First, a transparent conductive layer such as indium tin oxide (ITO) isdeposited and patterned to form common electrodes 20 and theirconnections 23. A film made of Cr, Al, Mo, Ti, Ta or their alloys aredeposited and patterned to form scanning signal lines 10. A gateinsulating film 40 made of such as silicon nitride is deposited to coverthe common electrode 20, the gate electrode 11 and the scanning signallines 10. An amorphous silicon layer and an n+ type amorphous siliconlayer are sequentially deposited on the gate insulating film 40, andpatterned to form the patterns 51, 52 and 60. A film made of Cr, Al, Moand Ta or their alloys are deposited and patterned to form a data wireincluding data lines 70, source electrodes 71, drain electrodes 72 andpixel electrodes 75. A portion of the n+ type amorphous silicon layerwhich is not covered by the data wire are removed. Next, a passivationfilm 80 is deposited and patterned to form an opening 81 on the displayregion. Finally, an aligning film 4 is coated thereon.

Next, a substrate for a liquid crystal display and a manufacturingmethod thereof according to the seventh embodiment are described indetail.

First, the structure of a liquid crystal display substrate is describedwith reference to FIGS. 35A to 35C. FIG. 35A is a layout view of a lowersubstrate of a liquid crystal display, and FIGS. 35B and 35C aresectional views taken along the lines VII1B-VII1B′ and VII1C-VII1C′respectively.

As shown in FIGS. 35A to 35C, a planar common electrode 20 made oftransparent conductive material such as ITO (indium tin oxide) is formedon a transparent insulating substrate 100. The common electrode 20 is ina pixel region, and is connected to adjacent common electrodes (notshown) in adjacent pixel regions via a plurality of connections 23 onthe substrate 100 to transmit common signals. A common signaltransmitter 24 on the substrate 100 is electrically connected to thecommon electrode 20 via the connection 23, and located near the rightedge of the substrate 100.

At the lower part of the pixel region, a gate line 10 is formed on thesubstrate 100 and extends in the transverse direction. The gate line 10is connected to a gate pad 12 which is located near the left edge of thesubstrate 100 and receives external scanning signals. A portion 11 ofthe gate line 10 serves as a gate electrode.

The common electrode 20, the connections 23, the common signaltransmitter 24, the gate line 10 and the gate pad 12 are made oftransparent conductive materials, and a redundant pattern for preventingtheir disconnection is formed on the upper part of the common electrode20, the connections 23, the common signal transmitter 24 and the gateline 10. A redundant connection 33 is provided on the connections 23 andupper part of the common electrode 20, a redundant common signaltransmitter 34 on the common signal transmitter 24, and a redundant gateline 30 and a redundant gate electrode 31 on the gate line 10 and thegate electrode 11, respectively. The redundant pattern 30, 31, 33 and 34may be made of any conductive material such as Al or Al alloy. However,when using Al or Al alloy, since direct contact of ITO and Al and Alalloy yields an oxide therebetween a buffer layer 32 and 35 made ofrefractory metal such as Cr or MoW alloy is interposed between the twolayers.

The common electrode 20 and the redundant pattern are covered with agate insulating layer 40. As shown in FIGS. 35A and 35B, a channel layer51 made of amorphous silicon is formed on the gate insulating layer 40opposite the gate electrode 11. Two separate portions 61 and 62 of acontact layer made of doped amorphous silicon heavily doped with n typeimpurity are formed on the channel layer 51 and located opposite eachother with respect to the gate electrode 11.

A data line 70 extending in the longitudinal direction is also formed onthe gate insulating layer 40 and intersects the gate line. A branch ofthe data line 70 extends to one portion 61 of the doped amorphoussilicon layer to form a source electrode 71, and a drain electrode 72 isformed on the other portion 62 of the doped amorphous silicon layer. Thegate electrode 11, the source electrode 71 and the drain electrode 72form electrodes of the TFT along with the channel layer 51. The dopedamorphous silicon layer 61 and 62 improves ohmic contact between thesource and the drain electrodes 71 and 72 and the amorphous siliconlayer 51.

The drain electrode 72 extends to form a plurality of linear pixelelectrodes 75 elongated longitudinally and a connecting portion 76 ofthe pixel electrodes 75. The data line 70, the source and the drainelectrodes 71 and 72 and the connecting portion 76 are covered with apassivation film 80, and the passivation film 80 and the gate insulatinglayer 40 having a contact hole 82 exposing the gate pad 12.

A portion of the passivation film 80 in the pixel region where the pixelelectrode 75 and the common electrode 20 are located may be removed toobtain sufficient electric field.

A method for manufacturing the LCD according to the seventh embodimentof the present invention is described in detail with reference to FIGS.36A to 39C. FIGS. 36A, 37A, 38A and 39A are layout views of theintermediate structures of the liquid crystal display substrateaccording to this embodiment, and FIGS. 36B and 36C, 37B and 37C, 38Band 38C, and 39B and 39C are sectional views taken along the lines VII2Band VII2C in FIG. 36A, VII3B and VII3C in FIG. 37A, and VII3B and VII3Cin FIG. 38A and VII4B and VII4C in FIG. 39A.

First, as shown in FIGS. 36A-36C, a transparent conductive layer such asindium tin oxide is deposited to the thickness of 50-100 nm on aninsulating substrate 100 and patterned using a first mask to form acommon wire including a common electrode 20, their connections 23 and acommon signal transmitter 24, and a gate wire including a gate line 10and a gate pad 12.

As shown in FIGS. 37A-37C, a lower conductive film made of a refractorymetal such as Cr or Mo-W, and an upper conductive film of Al or Alalloys with thickness of 100-400 nm are deposited in sequence andpatterned by using a second mask to form a redundant pattern 30, 33 and34 and a buffer layer 32 and 35 thereunder. A gate insulating layer 40is deposited thereon.

As shown in FIGS. 38A-38C, an amorphous silicon layer an n+ typeamorphous silicon layer are sequentially deposited on the gateinsulating film 40, and patterned by using a third mask to form thepatterns 51 and 60.

As shown in FIGS. 39A-39C, a film made of Cr, Al, Mo and Ta or theiralloys are deposited to a thickness of 100-200 nm and patterned by usinga fourth mask to form a data wire including data lines 70, sourceelectrodes 71, drain electrodes 72 and pixel electrodes 75. A portion ofthe n+ type amorphous silicon layer which is not covered by the datawire are removed.

Finally, a passivation film 80 with thickness of 200-400 nm is depositedand patterned along with the gate insulating layer 40 by using a fifthmask to form a contact hole 82.

Alternatively, the common wire and the gate wire are formed after theredundant pattern and the buffer layer is formed.

The material and the width of the electrodes 20 and 75 and the distancebetween the electrodes 20 may vary depending on the design of the liquidcrystal display. For example, if the pixel electrodes 57 aretransparent, the liquid crystal molecules over the pixel electrodes 57contribute to the display of images, causing larger transmittance. Incase of reflective liquid crystal display, the common electrode 20 andthe pixel electrodes 75 may be made of an opaque material having largereflectance.

Next, a substrate for a liquid crystal display and a manufacturingmethod thereof according to the eighth embodiment are described indetail.

The structure of a liquid crystal display substrate with reference toFIGS. 40 to 42. FIG. 40 is a layout view of a lower substrate of aliquid crystal display, and FIGS. 41 and 42 are different sectionalviews taken along the line VIIIA-VIIIA′.

As shown in FIGS. 40 to 42, a plurality of rectangular common electrodes20 made of transparent conductive material such as ITO (indium tinoxide) are formed on a transparent insulating substrate 100. Each commonelectrode 20 is in a pixel region, and is connected to adjacent commonelectrodes in adjacent pixel regions via a plurality of connections 23on the substrate 100 to transmit common signals. However, theconnections 23 may be eliminated.

A plurality of common electrode lines 33 located at the upper parts ofthe common electrodes 20 extends in the transverse direction toelectrically connect the common electrodes 20. The common electrodelines 33 have lower resistivity than the common electrodes 20, and arelocated either on the common electrodes 20 as in FIG. 41 or under thecommon electrodes 20 as in FIG. 42.

Between the common electrodes 20 adjacent along a column, a gate line 10is formed on the substrate 100 and extends in the transverse direction.A portion 11 of the gate line 10 serves as a gate electrode.

The common electrode lines 33 and the gate line 10 may be made of anyconductive material such as Al, Al alloy, Mo or Cr. However, when usingAl or Al alloy, since direct contact of ITO and Al and Al alloy yieldsan oxide therebetween, a buffer layer made of refractory metal such asCr or MoW alloy is interposed between the two layers.

The common electrodes 20 and the gate line 10 and the common electrodelines 33 covered with a gate insulating layer 40. As shown in FIGS. 41and 42, a channel layer 51 made of amorphous silicon is formed on thegate insulating layer 40 opposite the gate electrode 11. Two separateportions 61 and 62 of a contact layer made of doped amorphous siliconheavily doped with n type impurity are formed on the channel layer 51and located opposite each other with respect to the gate electrode 11.

A data line 70 extending in the longitudinal direction is also formed onthe gate insulating layer 40 and intersects the gate line 10. A branchof the data line 70 extends to one portion 61 of the doped amorphoussilicon layer to form a source electrode 71, and a drain electrode 72 isformed on the other portion 62 of the doped amorphous silicon layer. Thegate electrode 11, the source electrode 71 and the drain electrode 72form electrodes of the TFT along with the channel layer 51. The dopedamorphous silicon layer 61 and 62 improves ohmic contact between thesource and the drain electrodes 71 and 72 and the amorphous siliconlayer 51.

The drain electrode 72 extends to form a plurality of linear pixelelectrodes 75 elongated longitudinally and a connecting portion 76 ofthe pixel electrodes 75. The data line 70, the source and the drainelectrodes 71 and 72 and the connecting portion 76 are covered with apassivation film 80.

A plurality of isolated amorphous silicon patterns 52 are located at theintersections of the gate line 10 and the common electrode lines 33 andthe data lines 70, and interposed between the gate insulating layer 40and the data lines 70.

A method for manufacturing the LCD according to the eighth embodiment ofthe present invention is described.

In the case of the structure shown in FIG. 41, an ITO layer and a metallayer are deposited in sequence. The metal layer is patterned to formcommon electrode lines 33 and gate lines 10, and the ITO layer ispatterned to form common electrodes 20 and connections 23.

On the other hand, in the case of the structure shown in FIG. 42, ametal layer is deposited and patterned to form common electrode lines 33and gate lines 10. Thereafter, an ITO layer is deposited and patternedto form common electrodes 20 and connections 23. In this case, theconnections 23 may be eliminated.

Next, a gate insulating layer 40, an amorphous silicon layer 51 and adoped amorphous silicon layer 61 and 62 are deposited in sequence, andthe doped amorphous silicon layer and the amorphous silicon layer arethen patterned.

A metal film is deposited and patterned to form a data wire includingdata lines 70, source electrodes 71, drain electrodes 72 and pixelelectrodes 75. A portion of the n+ type amorphous silicon layer which isnot covered by the data wire are removed.

Finally, a passivation film 80 is deposited and patterned along with thegate insulating layer 40 to expose pads of the gate lines 10 and of thedata lines 70.

In this embodiment, since the common electrodes 20 are patterned byusing the common electrode lines 33 and the gate lines 10, misalignmentmay be reduced.

FIG. 43 shows a sectional view taken along the line VIIIB-VIIIB′ in FIG.40 but includes upper substrate. Among the regions between the pixelelectrodes 75 and the common electrodes 20, the regions S adjacent tothe data line 70 have disturbed electric field due to the signalsflowing through the data line 70. Accordingly, the liquid crystalmolecules in the regions S arrange themselves different from the otherregions, and light leakage may be generated.

The ninth embodiment suggests the structure reducing the light leakage.

FIGS. 44, 45 and 46 are sectional views of the liquid crystal displayaccording to the ninth embodiment of the present invention.

As shown in FIG. 44, a light blocking film 210 made of opaque materialsuch as Cr is formed on the upper substrate 200, and located at theposition corresponding to the regions S.

In addition to the light blocking film 210 on the upper substrate 200,another light blocking film 110 is formed between the data line 70 andthe pixel electrodes 70 adjacent thereto as shown in FIG. 45. The lightblocking films 110 are formed on both the lower substrate 100 and thecommon electrodes 20, covered with the gate insulating layer 40, andoverlap the data line 70.

It is preferable that the light blocking films 110 are conductive aswell as opaque to have a potential equal to the common electrodes 20. Inthis case, the light blocking films 110 block the electric field due tothe data line 70 as well as prevent light leakage in the region S.

FIG. 46 shows the structure having only light blocking film 120 on thelower substrate 100. The light blocking film 120 is formed on the gateinsulating layer 40 and covers the data line 70 at all and the pixelelectrodes in part. The light blocking film 120 in FIG. 46 is made ofinsulating material, preferably organic material, since it directlycontacts the data line 70 and the pixel electrodes 75.

The structures in the previous embodiments include a planar electrode,an insulating layer covering the planar electrode and a plurality oflinear electrodes on the insulating layer. However, the linear electrodemay be located under the planar electrode or may lie in the same plane.These structures are obtained by patterning the planar electrodes suchthat the planar electrode forms a continuous plane between the linearelectrodes. The planar electrode may overlap the linear electrode inpart. Otherwise, the planar electrode may not overlap the linearelectrode but the distance between the adjacent boundaries of the pixelelectrode and of the linear electrode is very close. The width of theplanar electrode is either equal to or larger than that of the linearelectrode. The liquid crystal molecules above the planar electrode areused for display, while the conventional IPS LCD uses the liquid crystalmolecules only above the regions between the electrodes.

FIG. 47 is a sectional view of an LCD according to the tenth embodimentof the present invention.

As shown in FIG. 10, a plurality of linear first electrodes 1 are formedon an insulating substrate 100, and the first electrodes 1 are coveredwith an insulating layer 3. A plurality of planar second electrodes 2are formed on the insulating layer 3, overlap the first electrode inpart, and have the width equal to or larger than that of the firstelectrode. The first and second electrodes 1 and 2 may be transparent oropaque according to the type of the LCD.

FIGS. 48, 49 and 50 shows an electric field, transmittance and viewingangle characteristic of the LCD according to the tenth embodiment,respectively.

When applying 0 V and 5 V to the first and the second electrodes 1 and 2respectively, the potential difference between the first and the secondelectrodes 1 and 2 yields the electric field shown in FIG. 48. In FIG.48, solid lines indicate equipotential lines, and dotted lines indicatethe lines of electrical force.

As shown in FIG. 48, the shape of the electrical field is symmetricalwith respect to the central lines of the first and second electrodes 1and 2, and similar to that shown in FIG. 2.

FIG. 49 illustrates the transmittance as a function of the appliedvoltage according this embodiment. As shown in FIG. 10, the thresholdvoltage is about 1.5 V, and the saturation voltage is about 5 V.

FIG. 50 is a graphical illustration showing the viewing anglecharacteristics according to this embodiment. As shown in FIG. 50, theboundary of the region where the contrast is equal to or more than 10 issubstantially over 60 degrees.

The LCD according to a eleventh embodiment of the present inventionhaving a thin film transistor as a switching element as well as theelectrodes suggested in the tenth embodiment, is described in detailwith reference to FIGS. 51 to 53.

FIG. 51 is a layout of a lower substrate of an LCD according to theeleventh embodiment of the present invention, wherein hundreds ofthousands of such pixels are formed in a matrix type in the LCD. FIGS.52 and 53 are sectional views taken along the lines XIA-XIA′ andXIB-XIB′, respectively.

A plurality of gate lines or scanning signal lines 10 and a gate pad 12are formed on a transparent insulating substrate 100. The gate line 10extends in the transverse direction and the gate pad 12 is connected tothe left end of the gate line 10. A portion 11 of the gate line 10serves as a gate electrode of a thin film transistor.

A plurality of common electrodes 20 elongated longitudinally are formedon the 100, and lies between the gate lines 10. A pair of transversecommon electrode lines 23 connecting the common electrodes 20 are alsoformed on the substrate 100.

The gate lines 10, the common electrodes 20 and the common electrodelines 23 are covered with a gate insulating film 40, and a channel layer51 made of amorphous silicon is formed on a portion of a gate insulatingfilm 40 opposite the gate electrode 11 of the scanning signal line 10.Two separated portions 61 and 62 of the doped amorphous silicon layerheavily doped with n-type impurity are formed on portions of the channellayer 51, and the portions 61 and 62 are opposite each other withrespect to the gate electrode 11.

On the other hand, a plurality of data lines 70 and a data pad 73 areformed on the gate insulating film 40. The data line 70 is elongatedlongitudinally to intersect the gate lines 10, and the data pad 73 isconnected to the upper end of the gate line 10. A branch of the dataline 70 extends to one portion 61 of the doped amorphous silicon layerto form a source electrode 71, and a drain electrode 72 is formed on theother portion 62 of the doped amorphous silicon layer. The gateelectrode 11, the source electrode 71 and the drain electrode 72 formelectrodes of the TFT along with the channel layer 51. The dopedamorphous silicon layer 61 and 62 improves ohmic contact between thesource and the drain electrodes 71 and 72 and the amorphous siliconlayer 51.

The data line 70, the data pad 73 and the source and the drainelectrodes 71 and 72 are covered with a passivation film 80. Thepassivation film 80 has contact holes 82, 83 and 84 exposing the gatepad 12, the data pad 73 and the drain electrode 84.

A plurality of linear pixel electrodes 91 elongated longitudinally and aconnecting portion 92 of the pixel electrodes 91 are formed on thepassivation film 80, and a redundant gate pad 95 and a redundant datapad 96 are also formed on the passivation layer 80. The boundaries 93 ofthe pixel electrodes 91 are over the common electrodes 20, and theconnecting portion 92 is connected to the pixel electrodes 91 andconnected to the drain electrode 72 through the contact hole 84. Thewidth of the pixel electrode 91 is equal to or larger than that of thecommon electrode 20. The redundant gate pad 95 and the redundant datapad 96 are connected to the gate pad 12 and the data pad 73 through thecontact holes 82 and 83, respectively.

A method for manufacturing the LCD according to the eleventh embodimentof the present invention is described in detail with reference in FIGS.51 to 53 and 54A to 57B.

First, as shown in FIGS. 54A-54B, a conductive layer made of arefractory metal such as Cr, Al, Mo, Ti, Ta or their alloys is depositedon an insulating substrate 100 and patterned using a first mask to forma common wire including a plurality of common electrodes 20 and commonelectrode lines 33, and a gate wire including a gate line 10 and a gatepad 12.

A shown in FIGS. 55A-55B, a gate insulating layer 40 of such as siliconnitride, an amorphous silicon layer and an n+ layer amorphous siliconlayer are sequentially deposited on the gate insulating film 40. The n+type amorphous silicon layer and the amorphous silicon layer patternedusing a second mask to form the channel layer 51 and a pattern 60.

As shown in FIGS. 56A-56B, a film made of Cr, Al, Mo and Ta or theiralloys are deposited and patterned by using a third mask to form a datawire including data lines 70, a data pad 73, a source electrode 71 and adrain electrodes 72. A portion of the n+ type amorphous silicon layerwhich is not covered by the data wire is removed.

A passivation film 80 with thickness of 200-400 nm is deposited andpatterned along with the gate insulating layer 40 by using a fourth maskto form contact holes 82, 83 and 84.

Finally, an ITO layer is deposited and patterned by using a fifth maskto form pixel electrodes 91, connecting members 92, a redundant gate pad95 and a redundant data pad 96.

An LCD according to a twelfth embodiment has pixel electrodes directlyon a gate insulating layer, as shown in the layout of FIG. 58. FIGS. 59and 60 are sectional views taken along the lines XIIA-XIIA′ andXIIB-XIIB′, respectively.

A plurality of pixel electrodes 92 are formed on a portion of a gateinsulating layer 40 between common electrodes 20 on an insulatingsubstrate 100. A drain electrode 72 on the gate insulating layer 40extends to connecting portion 92 of the pixel electrodes 91 and iselectrically connected to the pixel electrodes 91. A passivation film 80covers a data line 70, a source electrode 71 and the drain electrode 72on the gate insulating layer 40, and has an opening 81 in the displayregion in order to obtain sufficient electrical field.

A portion of the gate insulating layer 40 on a gate pad 12 connected toa gate line is removed to form a contact hole 41, and a redundant gatepad 95 on the gate insulating layer 40 is in contact with the gate padthrough the contact hole 41. A data pad 96 is formed on the gateinsulating layer 40 and the data line 70 extends to the data pad 96 tocontact the data pad 96. The passivation layer 80 has contact holes 82and 83 respectively exposing the redundant gate pad 95 and the data pad96.

The remaining structure is substantially the same as the eleventhembodiment.

A method for manufacturing the LCD according to the twelfth embodimentof the present invention is described in detail with reference to FIGS.58 to 60 and 61A to 63B.

Gate lines 10, a gate pad 12, common electrodes 91 and common electrodelines 23 are formed, a gate insulating layer 40, an amorphous siliconlayer and a doped amorphous silicon layer are deposited, and the dopedamorphous silicon layer 51 and the amorphous silicon layer 60 arepatterned as in the eleventh embodiment.

As shown in FIGS. 61A and 61B, the gate insulating layer 40 is patternedto form a contact hole 32 exposing the gate pad 12 by using a thirdmask.

As shown in FIGS. 62A and 62B, an ITO layer is deposited and patternedby using a fourth mask to form pixel electrodes 91, connecting members92, a redundant gate pad 95 and a data pad 96.

As shown in FIGS. 63A and 63B, a film made of Cr, Al, Mo and Ta or theiralloys are deposited and patterned by using a fifth mask to form a datawire including data lines 70, a source electrode 71 and a drainelectrodes 72. A portion of the n+ type amorphous silicon layer which isnot covered by the data wire is removed to form a contact layer 61 and62.

A passivation film 80 with thickness of 200-400 nm is deposited andpatterned by using a sixth mask to form contact holes 82 and 83 and anopening 81.

As described above, the method according to the twelfth embodimentrequires six masks. However, if eliminating the redundant gate pad, only5 masks are necessary.

The step of forming the pixel electrodes and the step of forming thedata wire in the twelfth embodiment are exchanged in a thirteenthembodiment. FIG. 64 is a layout view of an LCD according to thethirteenth embodiment of the present invention, and FIGS. 65 and 66 aresectional views taken along the lines XIIIA-XIIIA′ and XIIIB-XIIIB′,respectively.

The structure of the LCD in this embodiment is substantially the same asthat in the twelfth embodiment except that points that a connectingportion 92 is on a drain electrode 72 not under the drain electrode 72,a data pad 73 is made of the same layer as a data line 70, and aredundant data pad 96 is on the data pad 73.

A method for manufacturing the LCD according to the thirteenthembodiment of the present invention is substantially the same as that ofthe twelfth embodiment until the step of forming contact hole 32 in agate insulating layer 40.

As shown in FIGS. 67A and 67B, a film made of Cr, Al, Mo and Ta or theiralloys are deposited and patterned by using a fourth mask to form a datawire including data lines 70, a source electrode 71 and a drainelectrodes 72. A portion of the n+ type amorphous silicon layer which isnot covered by the data wire is removed to form a contact layer 61 and62.

As shown in FIGS. 68A and 68B, an ITO layer is deposited and patternedby using a fifth mask to form pixel electrodes 92, connecting members92, a redundant gate pad 95 and a data pad 96.

The step of forming a passivation layer is also the same as the twelfthembodiment.

The fourteenth embodiment suggests a structure having non-overlappingelectrodes.

FIG. 68 is a sectional view of an LCD according to the fourteenthembodiment of the present invention.

As shown in FIG. 69, a plurality of linear first electrodes 1 are formedon an insulating substrate 100, and the first electrode 1 are coveredwith an insulating layer 3. A plurality of planar second electrodes 2are formed on the insulating layer 3, and have the width equal to orlarger than that of the first electrode. The first and the secondelectrodes 1 and 2 do not overlap each other, but the distancetherebetween is very small.

The LCD according to a fifteenth embodiment of the present inventionhaving a thin film transistor as a switching element as well as theelectrode suggested in the fourteenth embodiment, is described in detailwith reference to FIGS. 70 and 72.

FIG. 70 is a layout of a lower substrate of an LCD according to thefifteenth embodiment of the present invention, and FIGS. 71 and 72 aresectional views taken along the lines XVA-XVA′ and XVB-XVB′,respectively.

Pixel electrodes 91 and common electrodes 20 do not overlap, but thedistance therebetween is very small. The remaining structure issubstantially the same as the eleventh embodiment. The manufacturingmethod is similar to that of the eleventh embodiment, and itsmodifications as in the twelfth and the thirteenth are possible.

The sixteenth embodiment suggests electrodes lying on the same layer.

FIG. 73 is a sectional view of an LCD according to the sixteenthembodiment of the present invention.

As shown in FIG. 73, a plurality of linear first electrodes 1 are formedon an insulating substrate 100, and a plurality of planar secondelectrodes 2 are formed on the substrate 100 and located between thefirst electrodes 1. The first and the second electrodes 1 and 2 do notoverlap each other, and the electric field is similar to that of thefirst embodiment.

The LCD according to a seventeenth embodiment of the present inventionhaving a thin film transistor as a switching element as well as theelectrode suggested in the fourteenth embodiment, is described in detailwith reference to FIGS. 74 to 76.

FIG. 74 is a layout of a lower substrate of an LCD according to thefifteenth embodiment of the present invention, and FIGS. 75 and 76 aresectional views taken along the lines XVIIA-XVIIA′ and XVIIB-XVIIB′,respectively.

A portion of a gate insulating layer 40 in the pixel region surroundedby gate lines 10 and data lines 70 is removed, and pixel electrodes 91lie between the common electrodes 20. The remaining structure issubstantially the same as the fourteenth embodiment. The manufacturingmethod is similar to that of the eleventh embodiment, and itsmodifications as in the twelfth and the thirteenth are possible.

The fourteenth embodiment suggests a structure having non-overlappingelectrodes.

FIG. 69 is a sectional view of an LCD according to the fourteenthembodiment of the present invention.

As shown in FIG. 69, a plurality of linear first electrodes 1 are formedon an insulating substrate 100, and the first electrodes 1 are coveredwith an insulating layer 3. A plurality of planar second electrodes 2are formed on the insulating layer 3, and have the width equal to orlarger than that of the first electrode. The first and the secondelectrodes 1 and 2 do not overlap each other, but the distancetherebetween is very small.

The LCD according to a fifteenth embodiment of the present inventionhaving a thin film transistor as a switching element as well as theelectrode suggested in the fourteenth embodiment, is described in detailwith reference to FIGS. 70 to 72,

FIG. 70 is a layout of a lower substrate of an LCD according to thefifteenth embodiment of the present invention, and FIGS. 71 and 72 aresectional views taken along the lines XVA-XVA′ and XVB-XVB′,respectively. Pixel electrodes 91 and common electrodes 20 do notoverlap, but the distance therebetween is very small. The remainingstructure is substantially the same as the eleventh embodiment. Themanufacturing method is similar to that of the eleventh embodiment, andits modifications as in the twelfth and the thirteenth are possible.

Now, embodiments having electrodes on the upper substrate as well asthose on the lower substrate will be described.

In the eighteenth embodiment, a planar electrode 2 is formed on a lowersubstrate 100 and covered with an insulating layer 3 as shown in FIG.77. A plurality of linear electrodes 1 made of Cr or ITO are formed onthe insulating layer 3. An upper electrode 250 is formed on an uppersubstrate 200. Since field strength is stronger, the response timebecomes short and the arrangement of the liquid crystal molecules isstable. Moreover, since the upper electrode 250 has an aperture 251causing fringe field, the arrangement of the liquid crystal moleculesvaries depending on the domains.

The planar and the linear electrodes 2 and 1 according to the ninthembodiment lie on the same plane as shown in FIGS. 78 and 79, and, inthis case, the upper electrode 250 according to the twentieth embodimenthas an aperture 251 as shown in FIG. 79.

In the meantime, as shown in the graph shown in FIG. 10, thetransmittance for the red and the green pixels is about 0.1 and that forthe blue pixels is about 0.08 which is lower than the red and the greenpixels by 20%. In order to reduce this difference between thetransmittance for respective pixels, the aperture ratio may be adjusteddepending on the color.

FIG. 80 shows a plan view of a black matrix for an LCD according to thetwenty-first embodiment. In FIG. 80, the reference numeral 210represents a black matrix which may be formed either on an uppersubstrate or on the lower substrate, and R, G and B indicates the red,the green and the blue pixels respectively. The area of the openings isdetermined by the relation TR*YR=TG*SG=TB*SB where TR, TG and TB aretransmittances for red, green and blue pixels and SR, SG and SB are thearea of the openings for red, green and blue pixels. As a result, theaperture ratio increases as the transmittance decreases.

As described above, the viewing angle can be widened, the drivingvoltage can be lowered down, and the aperture ratio can be increased.

Other embodiments of the invention will be apparent to the skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A liquid crystal display having a plurality ofpixels, comprising: first and second substrates facing each other; aplurality of first electrodes formed on the first substrate; a secondelectrode on the first substrate, the second electrode being insulatedfrom the first electrodes, overlapping the first electrodes at least inpart, and forming a continuous plane between the first electrodes; and athird electrode having an aperture formed on the second substrate,wherein a pixel has at least one of the first electrode and the secondelectrode.
 2. The liquid crystal display of claim 1, wherein the secondelectrode of a pixel is connected to adjacent pixels.
 3. The liquidcrystal display of claim 2, wherein both the first electrodes and thesecond electrode comprise transparent conductive material.
 4. The liquidcrystal display of claim 1, wherein either of the first electrodes andthe second electrode comprise transparent conductive material.
 5. Aliquid crystal display, comprising: first and second substrates oppositeeach other; a liquid crystal layer inserted between the first and thesecond substrates; first and second electrodes which are formed on thefirst substrate and electrically insulated from each other; and a thirdelectrode having an aperture formed on the second substrate, wherein arearrangement region, where molecules of the liquid crystal layer arerearranged by an electric field generated when voltages are applied tothe first and the second electrodes, is formed at least in part on thefirst or the second electrode, and a portion of the rearrangement regionformed on the first or the second electrode serves as part of a displayregion.
 6. The liquid crystal display of claim 5, wherein the moleculesin the rearrangement region have a twist angle and a tilt angle.
 7. Theliquid crystal display of claim 5, wherein the first electrode overlapsthe second electrode at least in part.
 8. The liquid crystal display ofclaim 5, wherein the electric field has parabolic lines of force locatedbetween the first electrode and the second electrode, and the electricfield on the first electrode or the second electrode has vertical andhorizontal components.
 9. The liquid crystal display of claim 5, whereinwidth of the first electrode is equal to or larger than width of thesecond electrode, and the rearrangement region on the first electrodeserves a part of the display region.
 10. The liquid crystal display ofclaim 9, wherein the first electrode is transparent.
 11. The liquidcrystal display of claim 10, further comprising first and secondpolarizing plates attached respectively to outer surfaces of the firstsubstrate and the second substrate, and wherein light passing throughone of the first and the second polarizing plates, passes through thedisplay region and reaches the other of the first and the secondpolarizing plates.
 12. The liquid crystal display of claim 5, whereinthe liquid crystal layer has either positive or negative dielectricanisotropy.
 13. The liquid crystal display of claim 12, wherein longaxes of liquid crystal molecules in the liquid crystal layer are eitherperpendicular or parallel to the first and the second substrates when novoltage is applied to the first and the second electrodes.